Thermoelectric generators



Oct. 11, 1955 P. L. BETZ 2,720,615

THERMOELECTRIC GENERATORS Filed Dec. 9, 1952 2 Sheets-Sheet l FLO. 2.

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INVENTOR I6" 2 5 n PaulL. B2153. 5 I3 le BY @Mnman,fm,mm ATTORNEYJ'WOct. 11, 1955 P. L. BETZ THERMOELECTRIC GENERATORS 2 Sheets-Sheet 2Filed Dec. 9, 1952 IN VENTOR TO CONTROL DEVICE TO CONTROL DEVICE Paul L.B815 (BMW, M wag/525w ATTORNEYS United States Patent Ofiice PatentedOct. 11, 1955 THERMOELECTRIC GENERATORS Paul L. Betz, Baltimore, Md.,assignor to Baltimore Gas and Electric Company, a corporation ofMaryland Application December 9, 1952, Serial No. 324,990

20 Claims. (Cl. 317-1335) This invention relates to thermoelectricgenerators suitable for use with safety or other devices for controllingfuel burners, and one aspect thereof is directed particularly toimprovements in such generators which decrease the time required foroperation of the associated device following extinction of the flamewhich activates the generator. The present invention has usefulcharacteristics in other respects than rapid decrease in electricaloutput upon cooling, and is therefore adapted to other applications thanthose involving the direct control of fuel burners.

By way of example, thermoelectric generators and their associated safetydevices for gas burners of the character heretofore commerciallyavailable are, in general, restricted to use in installations wherereasonably prompt operation of the safety device is acceptable followingextinction of the burner flame applied to the thermoelectric generator.With these devices, operation usually occurs in about 50 to 60 secondsafter flame failure; and in many appliances, such as Water heaters andresidential heating furnaces, as well as in some commercialapplications, a time delay of this magnitude between flame failure andsafetyoperation is not objectionable. However, there are many commercialtypes of gas burning apparatus, and certain domestic installations, towhich thermoelectric safety devices have not been applied because of theneed for faster operation than is obtainable with such devices aspreviously developed.

It is therefore one of the principal objects of the present invention toprovide improved forms of thermoelectric generators which are capable ofeffecting more rapid operation of the associated thermoelectricallycontrolled devices following interruption of heating than can beachieved by use of the thermoelectric generators of the prior art.

In conventional safety control systems for gas burners, a thermoelectricgenerator, such as a thermocouple, is positioned closely adjacent to apilot burner that is associated with a burner to be controlled so thatthe hot junction of the thermocouple is subjected to the heat of thepilot flame, and its cold junctions are connected to the energizingwinding of an electromagnetic safety device which, when energized by thethermoelectric current produced by the generator, holds an armature inattracted position. The armature is connected to a valve or othercontrol mechanism which is thereby maintained in running position topermit the flow of gas to the con trolled burner. In such aninstallation, when the pilot flame is extinguished, the hot junction ofthe thermoelectric generator cools by radiation, conduction and naturalconvection, augmented, in some instances, by the cooling effect of thestream of unignited gas flowing from the pilot burner. Cooling of thehot junction results in a gradual, although relatively rapid, reductionin the output voltage of the generator and a consequent reduction in thethermoelectric current supplied to the winding of the electromagneticsafety device. When the output current reaches a predetermined,relatively low value,

the electromagnet releases the armature of the safety device and permitsthe latter and its associated control mechanism to move to safetyposition and cut off the flow of gas to the controlled burner. Asindicated above, when using thermoelectric generators of the characterheretofore available, a period of approximately 50 to 60 seconds elapsesbetween failure of the pilot flame and operation of the safety device.

Other conventional arrangements include those in which thethermoelectric generator is heated by the flame at the burner controlledby the safety device, and those in which the flow of gas to the pilotburner as well as to the controlled burner is interrupted by the safetydevice upon cooling of the generator.

The improved thermoelectric generators of the present invention arecharacterized by the inclusion of elements having thermoexpansive orthermostatic characteristics which are employed to decrease or interruptthe output thermoelectric current of the generator and thereby effectdeenergization of the control or other device more rapidly than wouldresult from the decrease in thermoelectric current due to normal coolingof the hot junction of the generator.

The improved thermoelectric generators of the present invention may alsobe arranged so that the thermoexpansive or thermostatic elements willdecrease or interrupt the output thermoelectric current of the generatorupon heating of the thermostat above a predetermined value, in contrastwith the use in which the output cur-z rent is decreased or interruptedupon cooling of the generator thermostat. This arrangement is hence onein which an upper limit control action is provided. In otherapplications of the invention the desired characteristic may be theswitching action by which the generator may be disconnected fromassociated circuits when the temperature of the thermostat of thegenerator is either above or below a predetermined value depending onthe arrangement of the thermoexpansive or thermostatic elements.

One of the main objects of the invention is therefore to provide a novelform of thermoelectric generator which includes thermoelements havingdissimilar thermal expansion characteristics, as well as differentthermoelectric properties, and which utilizes the difference in thermalexpansion of said elements for modifying the output of thermoelectriccurrent from the generator.

A further object is to provide an improved control system for fuelburners which includes a thermoelectric generator subject to the heatproduced by the flame of a main or pilot burner for supplying current toan electromagnetic control device wherein the dissimilar thermalexpansion characteristics of said elements are employed for physicallyaltering circuit conditions in the thermoelectric circuit between thegenerator and the control device.

Another object is to provide a thermoelectric generator embodyingthermoresponsive or thermostatic means adapted to promptly decrease theeffective thermoelectric current output upon discontinuance of heatingof said generator, which generator also produces the less rapid butnevertheless certain normal decrease in thermoelectric current output inthe event that the thermoresponsive or thermostatic means becomesinoperative. I

Still another object is to provide a thermoelectric generator of novel,unitary construction in which the thermoelements serve the dual functionof generating thermoelectric current and providing a thermostaticcontrol of that current.

These, and other objects, including the provision of a quick-actingthermoelectric generator of simple, reliable construction, will appearmore fully upon consideration of the following detailed description ofthe several different embodiments of the invention which have beenillustrated in the accompanying drawings. It is to be expresslyunderstood, however, that these drawings are exemplary only and are notto be construed as defining the limits of the invention, for whichlatter purpose reference should be had to the appended claims.

In the drawings, wherein like reference characters indicate like partsthroughout the several views:

Fig. 1 is a schematic representation of one form of improvedthermoelectric generator embodying the invention wherein thethermostatically actuated contacts for controlling the flow ofthermoelectric current are connected in parallel with the output circuitof a thermocouple having thermoelements of different thermal expansioncharacteristics, the generator being applied to a control system forfuel burners;

Fig. 2 is a similar schematic illustration of a modification of thesystem shown in Fig. 1 wherein the thermostatically actuated contactsare connected in series with the thermocouple output circuit;

Fig. 3 is a longitudinal sectional view of a closed type thermoelectricgenerator constructed in accordance with the present invention, certainof the parts thereof being shown in full and the associated burner andcontrol device being illustrated diagrammatically;

Figs. 4 and 5 are transverse sectional views of the device shown in Fig.3 taken substantially on the lines 44 and 55 in the latter figure;

Fig. 6 is a view similar to Fig. 3 showing a modified form of closedtype generator wherein the thermostatically controlled contacts are inseries, instead of in parallel, with the thermocouple output circuit;

Fig. 7 is a view similar to Fig. 3 showing still another form of closedtype thermocouple embodying the invention wherein the thermostaticallyactuated contacts shunt the thermoelectric circuit to the control deviceupon extinction of the burner flame;

Fig. 8 is a schematic view of the generator portion of a system similarto that illustrated in Fig. 1 embodying a thermopile as the generator;and

Fig. 9 is a schematic view similar to Fig. 8 of a series arrangement ofthermopile and thermostatically controlled contacts comparable to thesystem of Fig. 2.

In each figure of the drawings, the thermostatically actuated contactsare shown in the position occupied thereby when the control system is inits normal running condition with the burner flame fully ignited andheating the generator in normal manner.

Referring now to Fig. 1, there is shown therein a thermoelectricgenerator 12 positioned closely adjacent to a fuel burner 11 so as to besubject to the heat produced by the flame thereof and an electromagneticcontrol device 13 having a magnetizable core 14, an energizing winding15 adapted to receive thermoelectric current from the generator 12through output leads 16 and 17, and an armature 18 to which is connectedan operating member 19. Operating member 19 serves in known manner tomove an associated control mechanism, such as a valve (not shown), to 2released position when winding 15 is deenergized, whereby one of thefollowing actions may be accomplished: (a) flow of fuel is discontinuedto burner 11, in which case burner 11 is the main burner; (b) flow offuel is discontinued to a main burner (not shown) but continued to pilotburner 11; (c) flow of fuel is discontinued to a main burner (not shown)and also to pilot burner 11, this action being commonly known as 100 percent shut-off. In the embodiment illustrated, the generator 12 consistsof an open type thermocouple embodying thermoelements 20 and 21 havingone end of each connected to one end of the other in overlappingrelation to form a hot junction 22, the opposite ends of thethermoelements, forming the cold junctions or output terminals 23 and 24of the thermocouple, being connected to output leads 16 and 17,respectively. Thermoelements 20 and 21 are joined together throughoutthe length of the overlapped hot junction 22 in any suitable manner, asby welding, and are made of any appropriate conductive metals havingdissimilar thermal expansion characteristics as well as differentthermoelectric properties, such as 18-8 stainless steel and constantanor Copel. The electromagnetic control device 13 of the associatedcontrol mechanism may conform to any of the various constructions nowknown to the art.

As thus far described (ignoring the overlapped character of hot junction22 and the dissimilar thermal expansion characteristics of thethermoelements), the arrangement of Fig. l is of conventionalconstruction and operates in known manner. As previously pointed out, itusually takes about 50 seconds or more after extinction of the burnerflame for the ordinary thermocouple to cool sufficiently to eflectoperation of the control device. In order to reduce this time interval,commonly referred to as the dropout time, the present invention combineswith the above described conventional type of control systemthermoresponsive or thermostatically operated means for deenergizing theelectromagnet winding of the control device more rapidly than wouldresult from normal cooling of the hot junction of the thermocouplefollowing flame failure.

In the embodiment illustrated in Fig. l, thermocouple 12 is mounted on abase 25, preferably formed of electrically insulating material, by meansof a clamp 26 which rigidly fixes the cold junction end of thermoelement21 to the base in position for connection of output terminal 24 tooutput lead 17. As shown, the thermocouple is of inverted U-shape, theportion of thermoelement 20 which depends from the overlapped hotjunction 22 being substantially parallel to, and free to move toward andaway from, the rigidly supported portion of thermoelement 21. The coldjunction or output terminal end 23 of thermoelement 20 is connected tooutput lead 16 by means of a flexible conductor 27.

With this arrangement, heating of hot junction 22 by the flame fromburner 11 not only generates thermoelectric current which is supplied tothe control device 13 through leads 16 and 17, but also causesdistortion in the overlapped ends of thermoelements 20, 21 andconsequent movement of the free portion of thermoelement 20 relative tothe fixed portion of thermoelement 21. If the coefficient of thermalexpansion of thermoelement 2 0 is greater than that of thermoelement 21,as it is assumed to be in the structure of Fig. 1, heating of hotjunction 22 produces movement of thermoelement 20 away fromthermoelement 21, the amount of movement being dependent for a giventemperature at hot junction 22 upon the respective coeflicients ofthermal expansion of the thermoelements, the length of thethermoelements and the length of their overlap at the hot junction.Cooling of hot junction 22 results in movement of the free end ofthermoelement 20 toward thermoelement 21. If the coeflicient of thermalexpansion of thermoelement 20 is less than that of thermoelement 21, orif the overlap is made with thermoelement 20 above thermoelement 21,instead of below as shown in Fig. 1 and with expansion coeflicients asfirst described, the direction of movement upon cooling will bereversed, i. e., thermoelement 20 will move away from thermoelement 21.

In accordance with the invention, the movement of the depending portionof thermoelement 20 relative to the substantially parallel, rigidlyfixed portion of thermoelement 21 is employed to actuate a pair ofelectrical contacts 28 and 29 which control the flow of thermoelectriccurrent to the output circuit of thermocouple 12. As shown,thermoelement 20 is provided with a member 30 having an arm 31 extendingtoward thermoelement 21 and on which is supported contact 28. Contact 29is supported closely adjacent contact 28, and is adjustable relativelyto the latter, by means of a screw 32 having threaded engagement with amember 33 which is suitably mounted on thermoelement 21. The physicalconnections betwen contacts 28, 29, their respective supporting meansand thermoelements 20, 21 are electrically conductive so that thecontacts form part of the thermoelectric circuit; for example, members30 and 33 may be brazed or silver soldered to thermoelements 20 and 21,respectively, and the connections between arm 31 and member 30, contact28 and arm 31, and contact 29 and screw 32 may be made in similarmanner. The relative positions of contacts 28, 29 may be adjusted bythreading screw 32 into or out of member 33, a lock nut 34 beingprovided for fixing the screw in adjusted position. Alternatively, thescrew 32 might be permanently fixed to member 33, after adjustment, bybrazing or soldering.

If desired, contacts 28, 29 may be protected against oxidation, or thepresence of foreign material that might interfere with their properoperation, by surrounding the contacts with a suitable enclosure forpreventing exposure thereof to the atmosphere surrounding the generator.For example, the contacts may be enclosed in a sealed metallic bellows35 having one end brazed or soldered to member 33 and the other endembedded in a bead 36 of glass or other suitable insulating materialwhich is fused to contact arm 31 intermediate contact 28 and member 30.

The parts of the generator shown in Fig. 1 are so arranged and adjustedrelative to one another that, when hot junction 22 is heated by theflame of burner 11 in normal manner, the resultant distortion of theoverlapped portions of thermoelements 20, 21 due to their differentthermal expansion characteristics causes the free portion ofthermoelement 20 to move away from thermoelement 21, to the left asviewed in Fig. 1, and to assume a position in which contact 28 isseparated from contact 29. The thermoelectric current generated bythermocouple 12 then flows to winding 15 of control device 13 throughleads 16, 17 and flexible conductor 27. Should the burner flame beextinguished, cooling of hot junction 22 distorts the overlappedportions of the thermoelements in the opposite direction and causesthermoelement to move toward thermoelement 21 and close contacts 28, 29,the structure being so designed and adjusted that closure of thecontacts is effected promptly after extinction of the burner flame andbefore release of armature 18 with normal cooling of hot junction 22.

When contacts 28, 29 are closed, a portion of the thermoelectric currentgenerated by thermocouple 12 is shunted through the circuit comprisingthermoelements 20, 21, members 30, 33, arm 31, screw 32 and contacts 28,29, thereby reducing the current flowing through output leads 16, 17 tothe winding 15 of control device 13. The electrical characteristics ofthe two circuits are so selected that the decrease in current flowthrough winding 15 upon closure of contacts 28, 29 is suflicient toeffect immediate release of armature 18 and movement of operating member19 to released position. Provision of the shunt circuit thus materiallyshortens the dropout time of control device 13 as compared withoperation of the conventional system. When burner 11 is reignited, thethermostatic action of the overlapped ends of thermoelements 20, 21opens contacts 28, 29 quickly and within the time required for thethermoelectric current generated by thermocouple 12 to build up to avalue at which the winding 15 of control device 13 is suflicientlyenergized to maintain armature 18 in its attracted running position.

The system illustrated in Fig. 2 is similar to that of Fig. 1 exceptthat the contacts 28, 29 are connected in series, rather than inparallel, with the output circuit of thermocouple 12, and the contactsupporting members are so mounted and adjusted that said contacts areclosed, rather than open, when the generator is heated normally by theflame of burner 11. To this end, member 33 is fixed to base instead ofthermoelement 21 and is suitably insulated electrically therefrom,output lead 16 is connected to member 33 instead of to the cold junctionof thermoelement 20, and contacts 28, 29' are so positioned that thethermostatically produced movements of contact 28 relative to contact29' are opposite to those produced by the device of Fig. 1. With thearrangement shown in Fig. 2, extinction of the burner flame results inopening of contacts 28, 29' which thereby completely interrupts the flowof thermoelectric current from thermocouple 12 to the winding 15 ofcontrol device 13 long before the hot junction 22 of the thermocouplehas cooled sufficiently to effect release of armature 18 in theconventional manner.

The thermoelectric generators illustrated in Figs. 1 and 2 are of theopen type in which both thermoelements are exposed to the action ofcombustion products from the burner flame at the hot junction. In manyinstances, such exposure may shorten the life of one of thethermoelements more rapidly than the other, in which case it isdesirable to protect the more susceptible thermoelement. The closed typestructures illustrated in Figs. 37 have therefore been provided forprotecting the more susceptible thermoelement from exposure tocombustion products by enclosing it within a hollow thermoelement madefrom the material that is the more resistant of the two to the action ofsuch products.

In the device shown in Figs. 35, an elongated thermoelement 37 made of amaterial to be protected from exposure to the action of combustionproducts, such as constantan or Copel, is enclosed within a hollowthermoelement 38 of a different, more resistant material, such as l88stainless steel, the upper end of the latter being closed by a plug 39which may be made of the same metal as outer thermoelement 38. Fixed toand depending from plug 39 is a relatively short thermoelement 40 whichalso may be of the same metal as thermoelement 38, but must be of aditferent metal than thermoelement 37, and towhich is secured inoverlapping relationship the upper end of inner thermoelement 37, theoverlapped portions of said elements forming an extended hot junction41. The junctions between inner thermoelement 37 and thermoelement 40and between the latter, plug 39 and outer thermoelement 38 may be madeby suitable welding procedures.

If desired, thermoelement 40 may be of a different material than outerthermoelement 38 and plug 39, such different material being selectedbecause of a more suitable thermal expansion characteristic. In thisevent, thermoelement 40 would form one thermojunction with plug 39 andanother with thermoelement 37. The temperature difference between thesetwo junctions would be small due to the relatively short length ofthermoelement 40. In any event, thermoelements 37 and 40 must havedissimilar thermal expansion characteristics in order to produce thethermostatic action which is characteristic of the present invention.

Fixed to the lower open end of outer thermoelement 38, as by brazing, isa conductive sleeve 42 to the lower end of which is connected, also bybrazing, a tubular lead member 43. Sleeve 42 serves as one of the outputleads of the thermoelectric generator. A conductor 44 is fixedlypositioned within tubular lead member 43 in coaxial relation therewithand electrically insulated therefrom by means of fixed spaced supportingblocks 45 and 46 of nonconducting material having forced fits withinmember 43. The upper end of conductor 44 is electrically connected toinner thermoelement 37 by a flexible conductor 47 and a contact block 48which is suitably fixed to the free, lower end of thermoelement 37, asby silver soldering or brazing. Conductor 47 comprises the other outputlead of the generator. The lower ends of tubular member 43 and thecoaxially arranged conductor 44 are connected to the energizing winding15 of electromagnetic control device 13 in any suitable manner, as byleads 16 and 17' which, if desired, may be arranged coaxially ascontinuations of member 43 and conductor 44, respectively. With thisconstruction, the central portions of concentric leads 43, 44 may bebent, if desired, to facilitate installation without disturbing the restof the structure or the electrical connections between the conductiveelements thereof.

Outer thermoelement 38 is illustrated as made in the form of athin-walled tube flattened into oval shape over the upper portion of itslength, as indicated in Fig. 4, plug 39 having a similar oval shape.This oval portion of thermoelement 38 provides an enclosure for extendedhot junction 41 having minimum heat capacity, and serves as the hotjunction end of the generator. The lower portion of thermoelement 38 maybe of circular section, as indicated in Fig. 5.

In order to provide the device of Figs. 3-5 with the improvedthermostatic control of the present invention, contact block 48 at thelower end of inner thermoelement 37 is provided with an electricalcontact 49 adapted to cooperate with a second contact 50 which is fixedto the inner end of a screw 51 adjustably threaded through a boss 52forming part of conductive sleeve 42. A lock nut 53 may be provided forfixing screw 51 and its contact 50 in adjusted position. Contact 50 issoldered or brazed to screw 51 and is thus electrically connected tosleeve 42. Since movable contact 49 is also electrically connected toinner thermoelement 37 through contact block 48, it will be evident thatthe two contacts are in parallel with the output leads of the generatorrepresented by sleeve 42 and flexible conductor 47.

As indicated in Fig. 3, the generator structure is adapted to be mountedclosely adjacent burner 11 so that the upper end thereof, which housesthe hot junction 41, may be subjected directly to the heat of the burnerflame. The coefiicients of thermal expansion of thermoelements 37 and 40are so selected and the overlapped hot junction 41 is so formed thatwhen the upper end of the generator is heated, the heat conductedthrough plug 39 to the hot junction causes distortion of the overlappedportions of the thermoelements in such directions that the free, lowerend of inner thermoelement 37 moves to the left, as viewed in Fig. 3,and assumes a position in which movable contact 49 is separated fromfixed contact 50. At the same time, heating of the hot junction 41generates thermoelectric current which flows through the circuitcomprising inner thermoelement 37, contact block 48, flexible outputconductor 47, conductor 44, lead 17 winding 15, lead 16', tubular leadmember 43, output sleeve 42, outer thermoelement 38, plug 39 andthermoelement 40.

When the burner flame is extinguished, hot junction 41 cools rapidly andthe overlapped portions of thermoelements 37 and 40 are so distorted asto deflect the lower end of thermoelement 37 to a position whereincontacts 49, 50 close, whereupon a portion of the thermoelectric currentproduced by the generator is shunted through the circuit comprisingcontacts 49, 50 and screw 51, and

the current flowing through leads 16, 17 is reduced below the valuerequired to maintain the armature 18 of control device 13 in attractedor running position. As in the case of Figs. 1 and 2, the thermalexpansion characteristics of thermoelements 37, 40 are so selected andthe parts of the device of Fig. 3 are so designed and adjusted thatcontacts 49, 50 are closed within the desired time period after theburner flame is extinguished so that the control device functions muchmore quickly than it would were it dependent solely upon normal coolingof the hot junction of the thermocouple for reduction of thethermoelectric current output.

The device illustrated in Fig. 6 is similar in construction to that ofFigs. 3-5, but differs from the latter in that the contacts 49, 50 areso arranged as to be closed, instead of open, when the upper end of thestructure is heated in normal manner by the flame of burner 11, and arein series, instead of in parallel, with the output circuit of thethermoelectric generator. To this end, contact 50 is mounted on a block54 having an insulated back 55 block 4 being fixed to the upper end ofan arm 56 (ill of conductive material which is fixedly positioned withinsleeve 42 and electrically insulated therefrom in any suitable manner,as by a supporting block 57 having a forced fit within the lower portionof sleeve 42'. The lower end of arm 56 is electrically connected to theupper end of conductor 44 by a flexible conductor 58. Sleeve 42 andflexible conductor 58 constitute the output leads of the generator. Asshown, contact is so positioned with respect to contact 49' that, uponapplication of heat to hot junction 41, the difference in thermalexpansion of the overlapped portions of thermoelements 40 and 37' causescontact 49 to move into engagement with contact 50' and thereby closethe circuit through which the thermoelectric current is supplied tocontrol device 13. The position of contact block 54 and contact 50 maybe adjusted in any suitable manner, as by means of adjusting screw 51which is threaded through boss 52 of sleeve 42' and bears at its innerend against the insulated back of block 54, it being understood that arm56 is sufficiently resilient to permit the desired adjusting movement ofsaid block.

In operation, the generator of Fig. 6 is directly comparable to that ofFig. 2 in that, when the parts are properly adjusted, normal heating ofhot junction 41 provides a closed circuit for the flow of thermoelectriccurrent to the control device through contacts 49, 50. Upon extinctionof the burner flame, contacts 49', 50' are opened promptly by thethermostatic movement of inner thermoelement 37 resulting from thecooling of hot junction 41, and thereby open the thermoelectric circuitand effect operation of the control device much more quickly than wouldbe possible in the absence of the thermostatic control.

The further modification of the invention illustrated in Fig. 7 issimilar to the devices of Figs. 1 and 3-5 in that it includesthermostatically actuated contacts which shunt the thermoelectriccircuit to the control device upon flame failure, but differs from allof the previously described constructions by relying upon the net linearthermal expansion of the thermoelements for thermostatic actuation ofthe contacts.

As shown in Fig. 7, the thermoelectric generator comprises an innerthermoelement 59 and an outer hollow thermoelement 60 of differentthermal expansion characteristics as well as different thermoelectricproperties, the upper end of outer thermoelement 60 being closed by ametallic plug 61 which is fixed thereto in any suitable manner, as bywelding. Inner thermoelement 59 is threaded at its upper end, asindicated at 62, for engagement with a similarly threaded, centrallypositioned aperture in plug 61, and has fixed thereto adjacent its lowerend a disk type contact 63 adapted to cooperate with an annular or ringtype contact 64 which is fixed to the inner wall of outer thermoelement60 at the lower end thereof just below contact 63. Contacts 63 and 64may be brazed or silver soldered in the positions shown in Fig. 7 withrespect to thermoelements 59 and 60 so as to be in good electricalcontact therewith.

In assembling the structure, inner thermoelement 59 may first beinserted in outer thermoelement 60 with contacts 63, 64 in the relativepositions shown in Fig. 7 and plug 61 may then be threaded onto theupper end of thermoelement 59 and positioned in the upper end ofthermoelement 60. Thereafter inner thermoelement 59 may be turned withrespect to plug 61 until contact 63 is brought into the desired positionrelative to contact 64 and be held in position by a lock nut 65 appliedto the outwardly extending end of thermoelement 59 to maintain the final'contact adjustment. If desired, thermoelement 59 and lock nut 65 may bewelded to plug 61 after the desired adjustment has been made.

The remainder of the generator comprises a conductive sleeve 66 fixed tothe lower open end of outer thermoelement 60, as by brazing, and atubular lead member 67 connected to the lower end of sleeve 66, also bybrazing. Conductor 68 is fixedly positioned within tubular lead member67 in coaxial relation therewith and electrically insulated therefrom bya non-conducting supporting block 69 having a forced fit within member67. The upper end of conductor 68 is electrically connected to the free,lower end of inner thermoelement 59 by a flexible conductor 70, therebeing either electrical insulation or a suitable air gap between theportion of thermoelement 59 below contact 63 and the surrounding wall ofthe opening in contact 64 through which the end of said thermoelementpasses. As in the previously described embodiments, the lowerends oftubular member 67 and the coaxially arranged conductor 68 are connectedto the energizing winding of electromagnetic control device 13 in anysuitable manner, as by leads 16 and 17' which, if desired, may bearranged coaxially as continuations of member 67 and conductor 68,respectively. Sleeve 66 and flexible conductor 70 constitute the outputleads of the generator.

In the structure of Fig. 7, outer thermoelement 6% is made of materialhaving a greater coefiicient of thermal expansion than that of innerthermoelement 59. Consequently, when the hot junction at 60, 61, 62, 59is heated in normal manner by the flame of burner 11, outerthermoelement 60 undergoes a greater linear expansion than innerthermoelement 59 and thereby causes contacts 63, 64 to separate so thatthe electrical output of the generator flows through sleeve 66, tubularlead member 67, flexible conductor 70, conductor 68 and leads 16', 17'to the winding 15 of control device 13. Upon extinction of the burnerflame, the net contraction of the thermoelements due to their differentthermal expansion characteristics is such as to close contacts 63, 64and thereby shunt the thermoelectric current produced by the generatoraway from the output circuit to the control device. Should thecoefficient of thermal expansion of outer thermoelement 60 be less thanthat of inner thermoelement 59, the same method of operation may beobtained by simply locating contact 63 below, instead of above, contact64.

It will be recognized that, where linear thermal expansion of thethermoelements is employed to actuate the contacts, as in Fig. 7, therelative movement of the contacts is necessarily less for a given hotjunction temperature than the movement obtainable in devices such asthose shown in Figs. l-6 where amplification of contact movement isobtained by reason of the length of thermoelement (Figs. 1 and 2) and 37or 37 (Figs. 3-6).

Figs. 8 and 9 illustrate diagrammatically how the invention may beapplied to systems wherein the thermoelectric generator consists of athermopile instead of a single thermocouple. As shown in Fig. 8, athermopile '71, having a series of thermoelements 72 and 73 of suitabledissimilar metals connected together to form hot junctions 74 and coldjunctions 74', is mounted in any convenient manner on a support 75 andis positioned closely adjacent burner 11 so that the hot junctions 74are all subjected to the heat produced by the burner flame. At theright-hand end of the series is a thermocouple of the type shown in Fig.1, comprising thermoelements 29 and 21 having an overlapped hot junction22, wherein the thermoelements perform the dual function of generatingthermoelectric current and of thermostatically actuating a pair ofcontrol contacts 28 and 29. As in the system of Fig. 1, contacts 28 and29 are electrically connected to leads 16 and 17, respectively, inparallel with the circuit by which the thermoelectric current generatedby the thermopile is supplied to a control device (not shown), and aremaintained in open position by the thermostatic action of thermoelements20 and 21 as long as hot junction 22 is heated in normal fashion.Inasmuch as the operation of the arrangement illustrated in Fig. 8 isthe same as that of Fig. 1 except for the presence of a plurality ofconventional thermocouples 72, 73, 74 in 19 series with thermocouple2t), 21, 22 embodying the thermostatic feature of the invention, adetailed description of said operation would appear unnecessary.

The device represented by Fig. 9 is similar to that of Fig. 8 exceptthat the contacts 28, 29, are connected in series, rather than inparallel, with the output of thermopile 71, and are so mounted andadjusted that they are closed, rather than open, when the generator isheated normally by the flame of burner 11. The arrangement of Fig. 9 isthus directly comparable to that of Fig. 2 and operates in the samemanner as the latter.

For purposes of illustration the drawings exemplify the use of thepresent invention to hasten the operation of an associated controldevice upon interruption of heating of the hot junction or junctions andof the thermostat. It is to be expressly understood, however, that thethermostats may be arranged to reduce or interrupt the thermoelectricoutput current when heating exceeds a predetermined value.

Other contemplated uses of the present invention include applications inwhich the switching action of the improved thermoelectric generator isthe desired function in that the generator may disconnect itself fromassociated circuits when the temperature of the thermostat is above orbelow a predetermined temperature depending on the arrangement of thethermostat.

There is thus provided by the present invention a new and improved formof thermoelectric generator which may be used with control devices forfuel burning apparatus, as well as with other devices, and whichmaterially decreases the time interval between interruption of heatingof the generator and operation of the associated control or otherdevice. The improvement resides primarily in the provision ofthermoelements having different thermal expansion characteristics aswell as different thermoelectric properties and in the combination withsuch thermoelements of means controlled by their thermostatic actionwhereby the output of thermoelectric current from the generator iseither decreased or interrupted promptly after failure of the flame orother source of heat and operation of the control device is effectedmore rapidly than would result from the decrease in thermoelectriccurrent due to normai cooling of the hot junction or junctions of thegenerator. The invention also provides structurally novel thermoelectricgenerators of the closed type incorporating the thermostatic controlfeature above mentioned.

Although several specifically different forms of the invention have beendescribed and illustrated in detail, it is to be expressly understoodthat these devices are intended for purposes of illustration only, andthat the inventive concept is capable of a variety of mechanicalembodiments. For example, it is obvious that the thermoelectricgenerator may incorporate any suitable combination of thermoelementshaving dissimilar thermoelectric and thermal expansion characteristics,and that the generator may be used with other forms of control device,or for other purposes, than herein represented. It is equally evidentthat the specific character and construction of the heat source withwhich the generator is associated is not material as long as itsimultaneously heats the hot junction of the thermocouple sufiicientlyto maintain an adequate output of thermoelectric current and producesthe desired thermostatic movement of the control contacts. In thisconnection, it will be understood that the generator may be used withelectrical as well as fuel burning sources of heat. It will also berecognized that the bellows enclosure of the contacts shown in Figs. 1and 2 isnot essential and may be modified or omitted, if desired, andthat the linear thermal expansion principle of Fig. 7 may be employed toactuate contacts in series, as well as in parallel, with the outputcircuit.

Various other changes, which will now suggest themselves to thoseskilled in the art, may be made in the mechanical construction,arrangement, electrical char-' acteristics and use of the device withoutdeparting from the inventive concept. Reference is therefore to be hadto the appended claims for a definition of the limits of the invention.

What is claimed is:

1. A thermoelectric device comprising thermoelements of dissimilarmetals forming a thermoelectric generator having at least one hotjunction and two free ends of dissimilar thermoelements, said one hotjunction being between adjacent thermoelements having different thermalexpansion characteristics as well as different thermoelectricproperties, said adjacent thermoelements of different thermal expansioncharacteristics being so constructed and arranged as to produce relativemovement between portions thereof remote from said one hot junction uponheating and cooling of said junction, output leads connected to the freeends of said thermoelements, and means actuated by the relative movementbetween said adjacent thermoelements for controlling the flow ofthermoelectric current in said leads.

2. A thermoelectric device comprising thermoelements of dissimilarmetals forming a thermoelectric generator having at least one hotjunction and two free ends of dissimilar thermoelements, said one hotjunction being between adjacent thermoelements having different thermalexpansion characteristics as well as different thermoelectricproperties, said adjacent thermoelements of different thermal expansioncharacteristics being so constructed and arranged as to produce relativemovement between portions thereof remote from said one hot junction uponheating and cooling and said junction, means for connecting the freeends of said thermoelements with the conductors of an output circuit,and contacts adapted to control the flow of thermoelectric current tosaid output circuit, said contacts being actuated between open andclosed positions by the relative movement between said adjacentthermoelements.

3. A thermoelectric device comprising thermoelements of dissimilarmetals forming a thermoelectric generator having at least one hotjunction and two free ends of dissimilar thermoelements, said one hotjunction being between adjacent thermoelements having different thermalexpansion characteristics as well as different thermoelectricproperties, said adjacent thermoelements of different thermal expansioncharacteristics being so constructed and arranged as to produce relativemovement between portions thereof remote from said one hot junction uponheating and cooling of said junction, output leads connected to the freeends of said thermoelements, and a pair of contacts connected inparallel with said leads for controlling the output of thermoelectriccurrent therefrom, said contacts being actuated between open and closedpositions by the relative movement between said adjacent thermoelements.

4. A thermoelectric device comprising thermoelements of dissimilarmetals forming a thermoelectric generator having at least one hotjunction and two free ends of dis similar thermoelements, said one hotjunction being between adjacent thermcelements having different thermalexpansion characteristics as well as different thermoelectricproperties, said adjacent thermoelements of different thermal expansioncharacteristics being so constructed and arranged as to produce relativemovement between portions thereof remote from said one hot junction uponheating and cooling of said junction, output leads conneted to the freeends of said thermoelements, and a pair of contacts connected in serieswith one of said leads for controlling the output of thermoelectriccurrent therefrom, said contacts being actuated between open and closedpositions by the relative movement between said adjacent thermoelements.

5. A thermoelectric device comprising a pair of thermoelements ofdifferent thermoelectric and thermoexpansive properties so connected toone another as to provide a combination thermostat and thermoelectricgenerator having a hot junction, the first of said thermoelements havinga portion free to move relatively to the second thermoelement wherebyheating and cooling of said junction produces movement of the freeportion of said first thermoelement relative to the secondthermoelement, and a pair of contacts for controlling the output ofthermoelectric current from said generator, one of said contacts beingoperated by the movable portion of said first thermoelement and theother contact being normally fixed with respect to said secondthermoelement.

6. A thermoelectric device comprising a pair of thermoelements ofdifferent thermoelectric and thermoexpansive properties so connected toone another as to provide a combination thermostat and thermoelectricgenerator having a hot junction, the first of said thermoelements havinga portion free to move relatively to the second thermoelement wherebyheating and cooling of said junction produces movement of the freeportion of said first thermoelement relative to the secondthermoelement, and a pair of contacts for controlling the output ofthermoelectric current from said generator, one of said contacts beingactuated by, and electrically connected to, the movable portion of saidfirst thermoelement and the other contact being normally fixed withrespect to, and electrically connected to, said second thermoelement.

7. A thermoelectric device comprising a pair of thermoelements ofdifferent thermoelectric and thermoexpansive properties so connected toone another as to provide a combination thermostat and thermoelectricgenerator having a hot junction, the first of said thermoelements havinga portion free to move relatively to the second thermoelement wherebyheating and cooling of said junction produces movement of the freeportion of said first thermoelement relative to the secondthermoelement, and a pair of contacts for controlling the output ofthermoelectric current from said generator, one of said contacts beingactuated by, and electrically connected to, the movable portion of saidfirst thermoelement and the other contact being normally fixed withrespect to, and electrically insulated from, said second thermoelement.

8. A thermoelectric device comprising a pair of thermoelements ofdifferent thermoelectric and thermoexpansive properties so connected toone another as to provide a thermoelectric generator having a hotjunction, the first of said thermoelements having a portion free to moverelatively to the second thermoelement whereby heating and cooling ofsaid junction produces movement of the free portion of said firstthermoelement relative to the second thermoelement, a pair of contactsfor controlling the output of thermoelectric current from saidgenerator, one of said contacts being actuated by the movable portion ofsaid first thermoelement and the other contact being normally fixed withrespect to said second thermoelement, and means forming an enclosure forsaid contacts to prevent exposure thereof to the atmosphere surroundingthe generator.

9. A thermoelectric device comprising a pair of thermoelements ofdifferent thermoelectric and thermoexpansive properties so connected toone another as to provide a combination thermostat and thermoelectricgenerator having a hot junction, the first of said thermoelements havinga portion free to move relatively to the second thermoelement wherebyheating and cooling of said junction produces movement of the freeportion of said first thermoelement relative to the secondthermoelement, a pair of contacts for controlling the output ofthermoelectric current from said generator, one of said contacts beingactuated by the movable portion of said first thermoelement and theother contact being normally fixed with respect to said secondthermoelement, and a sealed bellows enclosing, and electricallyinsulated from at least one of, said contacts to prevent exposurethereof to the atmosphere surrounding the generator.

10. A thermoelectric device comprising at least a pair of thermoelementsof different thermoelectric properties joined to provide athermoelectric generator having a hot junction and having their freeends separated from one another, one of said thermoelements being hollowand forming at least part of an enclosure for a second thermoelement, apair of contacts within said enclosure, the first of said contacts beingoperated by said second thermoelement and a second contact beingnormally fixed with respect to said one thermoelement, a conductorinsulated from said one thermoelement, and a conductive connectionbetween said conductor and one of said contacts, said thermoelementsalso having different thermal expansion characteristics and being soconnected together that the difference in thermal expansion thereofactuates said contacts upon heating and cooling of said hot junction.

11. A thermoelectric device comprising at least a pair of thermoelementsof different thermoelectric properties joined to provide athermoelectric generator having a hot junction and having their'freeends separated from one another, one of said thermoelements being hollowand forming at least part of an enclosure for a second thermoelement, apair of contacts Within said enclosure, the first of said contacts beingoperated by and electrically connected to said second thermoelement andthe second contact being normally fixed with respect to, andelectrically connected to, said one thermoelement, a conductor insulatedfrom said one thermoelement, and a conductive connection between saidconductor and said first contact, said thermoelements also havingdifierent thermal expansion characteristics and being so connectedtogether that the difference in thermal expansion thereof actuates saidcontacts upon heating and cooling of said hot junction.

12. A thermoelectric device comprising at least a pair of thermoelementsof different thermoelectric properties joined to provide athermoelectric generator having a hot junction and having their freeends separated from one another, one of said thermoelements being hollowand forming at least part of an enclosure for a second thermoelement, apair of contacts within said enclosure, the first of said contacts beingoperated by and electrically connected to said second thermoelement andthe second contact being normally fixed with respect to, andelectrically insulated from, said one thermoelement, a conductorinsulated from said one thermoelement, and a conductive connectionbetween said conductor and said second contact, said thermoelements alsohaving different thermal expansion characteristics and being soconnected together that the difference in thermal expansion thereofactuates said contacts upon heating and cooling of said hot junction.

13. A thermoelectric device comprising a first thermoelement at least aportion of which is of hollow construction, a second thermoelementhoused at least partially within said first thermoelement and connectedat one end to the latter to form a thermoelectric generator having a hotjunction, first and second output conductors for connecting said firstand second thermoelements to a utilization circuit, said first andsecond thermoelements having diiferent thermal expansion characteristicsand being so constructed and arranged that heating and cooling of saidhot junction produces relative movement therebetween, and means actuatedby the relative movement of said thermoelements due to the difference inthermal expansion thereof for controlling the flow of thermoelectriccurrent in said output conductors.

14. In a control system for fuel burners, a thermoelectric device havingat least one pair of thermoelements of different thermoelectricproperties connected together to provide a thermoelectric generatorhaving a hot junction subject to the heat produced by the flame at aburner, a safety device adapted to be energized by the thermoelectriccurrent produced by said generator, the said pair of thermoelements alsohaving difierent thermal expansion characteristics and being soconstructed and arranged that heating and cooling of said hot junctionproduces relative movement therebetween, and means actuated by therelative movement of said thermoelements due to the difference inthermal expansion thereof for controlling the flow of thermoelectriccurrent from said generator to said safety device.

15. In a control system for fuel burners, a thermoelectric device havingoutput terminals and at least one pair of thermoelements of differentthermoelectric properties connected together to provide a thermoelectricgenerator having a hot junction subject to the heat produced by theflame at a burner, a safety device adapted to be energized by thethermoelectric current produced by said generator, a circuit connectingthe output terminals of said thermoelectric device to said safetydevice, and a pair of contacts for controlling the flow ofthermoelectric current in said circuit, one of said contacts beingoperated by one of said pair of thermoelements and being movable by thelatter relatively to the other contact, said one thermoelement having adifferent coeflicient of thermal expansion from the other thermoelementwhereby heating and cooling of said thermoelements produces movement ofsaid one contact relative to the other contact.

16'. In a control system for fuel burners, a thermoelectric devicehaving output terminals and at least one pair of thermoelements ofdifferent thermoelectric properties connected together to provide athermoelectric generator having a hot junction subject to the heatproduced by the flame at a burner, a safety device having an energizingwinding connected to the output terminals of said thermoelectric device,the said pair of thermoelements also having different thermal expansioncharacteristics, and means controlled by the difference in thermalexpansion of said thermoelements for decreasing the flow ofthermoelectric current from said generator to said winding uponextinction of the burner flame.

17. In combination, a source of heat, a thermoelectric device havingoutput terminals and at least one pair of thermoelements of differentthermoelectric properties connected together to provide a thermoelectricgenerator having a hot junction subject to the heat produced by saidsource, a safety device connected to the output terminals of saidthermoelectric device and adapted to be energized by the thermoelectriccurrent produced by the generator when the heat source is producingheat, the said pair of thermoelements also having different thermalexpansion characteristics, and a pair of contacts actuated by therelative movement of said thermoelements due to the difference inthermal expansion thereof for deenergizing said safety device when theheat source ceases to produce heat.

18. In combination, a source of heat, a thermoelectric device havingoutput terminals and a pair of thermoelements of differentthermoelectric properties connected together to provide a thermocouplehaving a hot junction subject to the heat produced by said source, asafety device connected to the output terminals of said thermoelectricdevice and adapted to be energized by the thermoelectric currentproduced by said thermocouple when the heat source is producing heat,the thermoelements of said thermocouple also having different thermalexpansion characteristics, and means comprising a pair of contactsactuated by the relative movement of said thermoelements due to thedifference in thermal expansion thereof for decreasing the flow ofthermoelectric current from said thermocouple to said safety device whenthe heat source ceases to maintain the hot junction of said thermocouplewithin a desired temperature range.

19. In combination, a source of heat, a thermoelectric device havingoutput terminals and a pair of thermoelements of differentthermoelectric properties connected together to provide a thermocouplehaving a hot junction subject to the heat produced by said source, asafety device connected to the output terminals of said thermoelectricdevice and adapted to be energized by the thermoelectric currentproduced by said thermocouple when the heat source is producing heat,the thermoelements of said thermocouple also having ditferent thermalexpansion characteristics, and means comprising a pair of contactsactuated by the relative movement of said thermoelements due to thedifierence in thermal expansion thereof for opening the thermoelectriccircuit between said thermocouple and said safety device when the heatsource ceases to maintain the hot junction of said thermocouple within adesired temperature range.

20. In combination, a source of heat, a thermopile having outputterminals and a plurality of pairs of thermoelements connected togetherto provide a plurality of thermocouples having hot junctions all subjectto the heat produced by said source, the thermoelements of at least oneof said pairs having different thermal expansion characteristics, asafety device connected to the output terminals of said thermopile andadapted to be energized by the thermoelectric current produced therebywhen the 16 heat source is producing heat, and means comprising a pairof contacts for controlling the flow of thermoelectric current from saidthermopile to said safety device, said contacts being actuated by therelative movement of said one pair of thermoelements due to thedifierence in thermal expansion thereof.

References Cited in the file of this patent UNITED STATES PATENTS2,040,217 Smulski May 12, 1936 2,102,407 Dann Dec. 14, 1937 2,183,855Mansky Dec. 19, 1939 2,268,960 Ray Jan. 6, 1942 2,385,530 Paille Sept.25, 1945 2,449,185 Unger Sept. 14, 1948 FOREIGN PATENTS 680,611 GermanySept. 2, 1939

